1. Field of the invention
The present invention relates generally to devices and methods for treating spinal disorders and more specifically to a fixation assembly for retaining vertebrate endoskeletal members in a desired fixed spatial relationship.
2. Description of the Background
A variety of devices are known for the fixation of endoskeletal members or bones in humans and animals. Fixation of bones may be temporary in order to allow for normal healing, as with a break in the long bones of the limbs, or permanent in order to provide support and alignment of the skeletal members. The latter is often the case with respect to the vertebrae of a spinal column where support and spatial fixation are necessary due to injury or disease. Even where vertebral or spinal healing occurs after fixation, the fixations means or devices, which include bone fastener assemblies, often remain in position for life.
Bone fastener assemblies utilized in conjunction with spinal fixation often include a pedicle screw assembly or assemblies that are anchored by threaded engagement into the pedicle of each of the vertebrae that are to be maintained in a desired spatial relationship. One or more longitudinal supports, which may comprise plates or rods that extend generally longitudinally along the spinal column, are connected securely to the pedicle screw assemblies in a manner that allows the vertebrae to be maintained in a desired alignment. In order to achieve the desired stability, the bone fasteners must be attached securely to the vertebrae and connected firmly to the appliance.
A variety of means have been utilized to connect the rods or plates to the pedicle screws or other bone fasteners. The secure placement and alignment of a rod between pedicle screws or the placement of a plate linking two or more rigid screws can be difficult due to the angular orientation of the screws and exacerbated by any deformity of the spinal column. Precise alignment with all of the bone fasteners and secure connections are desirable to decrease the possibility that unanticipated and undesired stresses can cause the bone bodies or vertebrae to fracture or the screws to loosen over time. It is, therefore important that bone fastener assemblies be provided that minimize the likelihood of the establishment of undesirable stresses.
Thus, it is an object of the present invention to securely place, retain and align a rod or plate with a pedicle screw or screws over the primary longitudinal axis of the pedicle screw in order to minimize the likelihood of the establishment of undesirable stresses.